This is an optional KDE Direct Vertical Stabilizer Mount, and is intended for use with the Align T-Rex 250 and 250 Pro helicopters. The KDE Vertical Stabilizer Mount Upgrade provides a strong connection between the tail boom and tail case for the T-Rex 250 helicopters. With a precision CNC machined cylindrical pin, the upgrade provides an accurate, perpendicular installation of the tail components to the main shaft for unparalleled flight performance.